1. Field of the Invention
The present invention relates to a technique for holding a substrate with a dielectric chuck and conveying the held substrate.
2. Description of the Related Art
For a semiconductor manufacturing process, a projection EUV exposure system is proposed in that a reticle pattern is projected and transcribed on a silicon wafer using EUV (extreme ultraviolet) light with a wavelength of 13 to 14 nm as light exposure.
The disclosed EUV exposure system will be described with reference to FIG. 8. A reticle 306A has a device pattern drawn thereon. A vacuum chamber 303 forms a vacuum region. The reticle 306A is mounted on a reticle stage 306. A reticle lock 320 is used when the reticle 306A is conveyed into the vacuum chamber 303. A reticle changer hand 313 is used for conveying the reticle 306A. A reticle stocker 312 is for storing the reticle 306A within the vacuum region.
In such a conventional exposure system, the reticle 306A passed through the load lock 320 is conveyed to the reticle stocker 312 in the vacuum region with the reticle changer hand 313. Furthermore, the reticle changer hand 313 conveys the reticle 306A in the reticle stocker 312 to the reticle stage 306 so as to expose the reticle 306A with light.
As for conveying a reticle within an exposure system, a unit for vacuum attracting the bottom surface of a reticle is disclosed in Japanese Patent Laid-Open No. 05-278813. As for conveying a reticle in the vacuum region, a hand for electrostatically attracting the reticle is disclosed in Japanese Patent Laid-Open No. 2001-315085, No. 2000-031252, and No. 2002-203837.
However, in the above-mentioned conveying units, there has been a problem that an original plate (reticle) drops and is damaged during conveying. That is, under a vacuum condition as in the EUV exposure system, even when the reticle bottom surface is vacuum-suctioned as disclosed in Japanese Patent Laid-Open No. 05-278813, the pressure difference is small so that sufficient adsorption power for conveying the reticle cannot be obtained. The reticle used in the EUV exposure system is generally made of glass, so that by the electrostatic chuck as disclosed Japanese Patent Laid-Open No. 2001-315085, No. 2000-031252, and No. 2002-203837, sufficient adsorption power for conveying the reticle cannot be obtained. Furthermore, since a conductive film as a pattern film is formed on the bottom surface of the reticle used for the EUV exposure system, although the conductive film can be chucked with the electrostatic chuck, the adsorption power is different depending on the film material and the film quality, so that the reticle may drop and be damaged during conveying.